The present invention relates generally to an Instantaneous Frequency Measurement (IFM) receiver system with two signal capability.
An IFM receiver can have very wide bandwidth, and generate fine frequency information on a short pulsed signal. It also has small size and light weight. Although it has all the desired properties required for Electronic Warfare (EW) applications, it has one major deficiency: that is, the IFM receiver can not process simultaneous signals. Theoretically, an IFM receiver can be designed to work with simultaneous signals such as discussed in U.S. Pat. No. 4,977,365 by James B.Y. Tsui and William S. McCormick for an "Instantaneous Frequency Measurement (IFM) Receiver to Measure Frequency and Angle of Arrival (AOA of Multiple Signals", issued Dec. 11, 1990. The approach used in that patent has the following characteristics: To actually design an IFM receiver with that method, one needs many mathematical operations using number theory and the Chinese remainder theorem which might be difficult to implement in hardware. The delay lines selected to achieve the multiple signal IFM receiver are different from those used in conventional IFM receivers. One of the most important factors is the predicted dynamic range of the IFM receiver. When two signals are within 6 dB, the receiver will detect both signals. When the two signals are separated by more than 6 dB the receiver will receive the stronger one and miss the weak one. Therefore, the maximum dynamic range for two signals will be approximately 6 dB which is inadequate for most EW applications.
______________________________________ The following United States patents are of interest. ______________________________________ 4,633,516 Tsui 4,757,253 Weber et al 4,791,360 Gagnon et al 4,963,816 Tsui et al 4,992,747 Myers 4,977,365 Tsui et al ______________________________________
The Tsui patent 4,633,516 discloses an instantaneous frequency measurement receiver having a digital format for supply to the utilization circuits 26 and is an improvement over conventional (prior art) receivers shown in FIG. 1. The circuit includes a 90.degree. hybrid and A/D converters. The input signal from the amplifier-limiter combination 12 passes through hybrid 34. The two A/D converters 36, 38 digitize the outputs at time t.sub.1 and then at time (t.sub.1 +r). If the A/D converters are too slow to sample at a time r apart, then four A/D converters 56-59 can be used. In that case, converters 56, 58 will sample at t.sub.1 and the other two 57, 59 will sample at time (t.sub.1+ r). The equations are disclosed.
Weber et al disclose a circuit arrangement for frequency analysis of received signals which lie in a wide overall frequency band. Circuit details of the filter bank, frequency modulators, transmission channels, and the transmission paths are disclosed.
Gannon et al disclose a method for simultaneous signal frequency measurement, wherein simultaneous signals of similar amplitude are received and successively applied to a plurality of either frequency or time dependent signal modifying circuits, via switching circuitry. Respective ones of the received signals are separated with respect to frequency in one of both of amplitude and time from one another via the signal modifying circuits, which can be low pass and high pass filters, or positive and negative dispersive delay lines. The frequency information relating to the weaker signals is not lost. The signals need not have comparable amplitudes or coincident leading edges. Quantizer circuits 39A, 39B and 39C are provided for digitizing and encoding the outputs of the respective differential amplifier and detector circuits 37A, 37B and 37C and generating digital signals representative of the input signal frequency in response thereto. Several alternative designs are disclosed.
Tsui et al patent 4,963,816 discloses an instantaneous frequency measurement receiver with only two delay lines. The algorithm for achieving frequency resolution is based on the Chinese remainder theorem.
Myers discloses the multiple reuse of an FM band wherein a signal receiving system is utilized for receiving messages from each of several unequal amplitude FM carriers occupying the same portion of the frequency band.